1. Field of the Invention
The present invention relates generally to the use of cardiac glycosides such as oleandrin to inhibit the secretion of IL-8 from cells secreting elevated levels of IL-8.
2. Background of the Technology
Cystic fibrosis is the most common autosomal recessive lethal disease in the United States (Welsh, et al. (1995)). Approximately 5% of the population carries one mutant CFTR gene (Rommens, et al. (1989); Riordan, et al. (1989); Kerem, et al. (1989)), and the disease occurs in a frequency of 1 in 2500 live births. Statistically, death occurs in the majority of patients by age 28. At the present time the respiratory difficulties and ensuing complications of inflammation and lung infection are directly responsible for the eventual death of over 90% of CF patents. In control individuals, inflammation is regulated by well-characterized signaling pathways. However, in CF inflammation is out of control, eventually causing destruction of the lung. The consequences are terminal if a lung cannot be found for transplantation.
The CF lung has been described as microscopically normal at birth, with subtle abnormalities in mucus secretion appearing very early (Pilewski, et al. (1999)). Bacterial infection and objective evidence of inflammation occur at later times, with a clear temporal evolution of different principal bacterial pathogens. For example, Staphylococcus aureus and Hemophilus influenzae take up residence in the CF airway early, the mean age of positive culture being 12.4 months (Abman, et al., 1991). By comparison, Pseudomonas aeruginosa infection follows at a substantially later time, the mean age of first positive culture being 20.8 months. Persistent colonization by P. aeruginosa characterizes the older CF patient, and profound, persistent cellular evidence of inflammation accompanies persistent infection as the patient approaches the terminal phases of the disease.
As the CF patient ages, the CF lung becomes characterized by elevated levels of white cells. These include polymorphonuclear leukocytes, macrophages, monocytes, lymphocytes and eosinophils. It is hypothesized that these cells are attracted from the circulation into the airway by the high levels of interleukin-8 (IL8) and other pro-inflammatory factors such as IL-1β, IL-6, leukotriene, B4, RANTES, and TNFα. These factors mark the character of the CF lumenal milieu (Bonfield, et al, (1995a); ibid (1995b)). Among these factors, IL-8 ranks as the most prevalent and potent. IL-8 is an 8 kDa chemokine protein which is a principal chemotactic agent for neutrophils and T cells (Cruse, et al. (1995)). This chemokine is of specific importance for cystic fibrosis because it is profoundly elevated in bronchoalveolar lavage fluids, sputum, and serum from CF patients (Dean, et al. (1993); Richman-Eisenstat, et al. (1993); Francoeur, et al. (1995); Armstrong, et al. (1997)). It had been considered possible that high IL-8 levels might be secondary to chronic or persistent infections. However, both IL8 message and protein are elevated in bronchoalveolar lavage fluids from infants with CF as early as 4 weeks of age (Khan, et al. (1995)). Importantly, hypersecretion of IL-8 occurs prior to objective evidence of infection by viruses, fungi or common CF pathogenic bacteria (Khan, et al (1995)). The concept of the generality of a pro-inflammatory state for CF epithelia is further manifest by the fact that fecal. IL-8 levels in CF children are approximately 1000-fold elevated over non-CF controls (Briars, et al. (1995)). Fecal IL-8 levels are correlated with lung function (FEV1, forced expiratory volume in one second), and only to some extent with established Pseudomonas infection. A recent study with bronchial biopsies from CF patients undergoing lung transplant has demonstrated consistent up-regulation of IL-8 expression in submucosal gland cells (Tabary, et al. (1998)). Thus, based on these clinical criteria, high IL8 levels would appear to be intrinsic to the CF lung.
Consistently, airway epithelial cells isolated from CF patients secrete more IL-8 than do cells cultured from patients without CF (Bedard, et al. (1993); Ruef et al. (1993); Dimango, et al. (1998)). Interestingly, cells cultured from much higher in the airway, such as those from the nasal epithelium, do not show this disparity between control and CF patients (Black, et al, (1998)). In addition, CF respiratory epithelial cells are hyper-responsive in terms of IL-8 secretion to Pseudomonas cells and toxins (Massion, et al. (1994); Dimango, et al. (1998)), or to a combination of TNFα and INFγ (Schweibert, et al. (1999)). CFTR levels in human lung are highest in submucosal glands. High levels of IL-8 mRNA and protein have been shown in these tissues from CF patients, both in vitro and in vivo (Tabary, et al. (1998)). In the latter study, other pro-inflammatory cytokines such as IL-1β and IL-6 were unaffected by the CF condition. The high levels of IL-8 production by CF epithelial cells have been proposed to be due to retention of mutant CFTR in the endoplasmic reticulum, which, by an unknown mechanism, activates NFκB via activation of IκB (DiMango, et al. (1998)). Attention is drawn to the NFκB system because it is known that transcription of the IL-8 gene is activated in normal epithelial cells when activated NFκB migrates from the cytosol to the nucleus and binds to the IL-8 promotor. An adenovirus hyperexpressing IkBα has been employed to suppress IL-8 secretion both from a CF cell line (“CFTE”), as well as from mouse lung (as MIP2), when instilled simultaneously with an infectious dose of P. aeruginosa (Griesenbach, et al. (1999); ibid (2000).
It would be desirable to develop compositions that reduce the secretion of IL-8 and other pro-inflammatory cytokines from cells secreting elevated levels of these compounds. These compositions could be useful in the treatment of disease conditions characterized by elevated levels of these compounds.